session = null after postback

Very simple login page... i was getting viewstate corruption errors off a page with only 5 small server controls (boxes, labels, and a button), so I replaced them with traditional form inputs. I was still getting an error, so i stepped through, and Session was showing as null, and an error was throwing when i tried to use it in an op. the strange thing is, request.servervariables["script_name"] was also evaluating to null. Nothing else, as far as ASP objects, is evaluating to null... i can use all the other items in request.servervariables, i can use response, server, application....

and to top it all off, "IsPostBack" is always evaluating to false, even after the page is submitted and the request.form variables processed !

UGH.

i got no useful help at the asp.net forums, so hopefully someone here has dealt with this before =(